1. Field of the Invention
The invention relates to a vehicle control system that is configured to control behavior characteristics or acceleration/deceleration characteristics (which will be called “running characteristics”) of the vehicle, such as a power characteristic, steering characteristic and a suspension characteristic of the vehicle, so that the running characteristics match a running environment and driver's preferences and intention regarding running.
2. Description of the Related Art
While the vehicle behavior, such as a vehicle speed and a running direction, varies according to the driver's accelerating/decelerating operation and steering operation, the relationship between the amount of the driver's operation and the amount of change of the behavior is determined not only by the energy efficiency, such as a fuel efficiency, but also by characteristics, such as a ride comfort, quietness and power performance, which are required of the vehicle.
In the meantime, environments in which the vehicle runs include a wide variety of surroundings or road types, such as an urban area, an expressway, a winding road, an uphill, and a downhill, and there are a variety of driver's preferences and intentions regarding running, and there are a variety, of impressions the driver receives from the vehicle during running. Therefore, an expected running characteristic is not necessarily obtained if the running environment changes or the vehicle is driven by another driver. As a result, so-called driveability may deteriorate.
Thus, one type of vehicle has been developed which is arranged to manually select running characteristics, such as a power output characteristic (or acceleration characteristic) and a suspension characteristic, concerning the behavior of the vehicle, by operating a mode selection switch. Namely, the vehicle is arranged to manually select a drive mode from, for example, a sporty mode in which the vehicle runs with an excellent accelerating ability, and the suspension is set to be somewhat hard, a normal mode in which the vehicle accelerates at a relatively low rate, and has a relatively soft suspension characteristic, and an eco mode in which the fuel economy or efficiency is prioritized, by operating the switch.
Also, various systems have been proposed which are configured to cause the driving orientation to be reflected by behavior control of the vehicle. This type of system does not necessitate any switching operation, and permits changes of subtle or detailed characteristics. One example of this type of system is described in Japanese Patent Application Publication No. 06-249007 (JP-A-06-249007). In the system described in JP-A-06-249007, which is a driving force control system using a neurocomputer, the relationship of the acceleration with respect to the acceleration stroke and the vehicle speed is learned as a required acceleration model, and the throttle opening is calculated based on a deviation between the, model and a second reference acceleration model that reflects the driver's orientation or preferences in connection with running, and a deviation between the second reference acceleration model and a first reference acceleration model as a standard model.
Also, a system that is configured to detect the driving characteristics or driving orientation while distinguishing those of the longitudinal direction of the vehicle from those of the lateral direction is described in Japanese Patent Application Publication No. 11-129924 (JP-A-11-129924). The system described in JP-A-11-129924 obtains an acceleration/braking model of the driver, based on control input information, such as the amount of operation of the accelerator pedal or brake pedal, and behavior information, such as a longitudinal acceleration, and also obtains a steering model of the driver, based on lateral operation information, such as a steering angle, and lateral behavior information, such as a yaw rate.
Both of the systems described in JP-A-06-249007 and JP-A-11-129924 are configured to detect the relationship between the amount of operation performed by the driver and the amount of change of the vehicle behavior achieved by the driver's operation. Like these systems, a system configured to estimate the driving orientation or preferences using variables associated with driving operations, which are derived from the driver's operations, is described in Japanese Patent Application Publication No. 09-242863 (JP-A-09-242863). More specifically, the system described in JP-A-09-242863 is configured to estimate the driving orientation of the vehicle, based on the output of a neural network that receives at least one of the amount of output operation at the time of start of the vehicle, the maximum rate of change of the output operation amount, the maximum deceleration during braking of the vehicle, coasting time of the vehicle, and the constant-vehicle-speed running time.
On the other hand, a system configured to cause the driving orientation and road conditions to be reflected by shift control is described in Japanese Patent Application Publication No. 07-156815 (JP-A-07-156815). The driving orientation is denoted as “crispness” in JP-A-07-156815, and, the crispness representing a driving condition of the driver is estimated by obtaining the frequency distribution for each of vehicle operating parameters including the vehicle speed, accelerator pedal stroke, and the longitudinal acceleration and lateral acceleration of the vehicle, and entering the average value and distribution of each frequency distribution into a neural network.
A driving force control system that aims at performing driving force control that more accurately reflects the driver's intention represented by the amount of operation of the vehicle is described in Japanese Patent Application Publication No. 2008-120172 (JP-A-2008-120172). The system described in JP-A-2008-120172 is configured to control the vehicle speed based on the actual vehicle speed, and a target vehicle speed set based on the driver's intention, and change the manner of controlling the vehicle speed according to the lateral acceleration, such that the degree of the change is changed based on a relative vehicle speed between the actual vehicle speed and the target vehicle speed.
A shift control system configured to accurately determine a driver's intention regarding running and perform shift control that reflects the driver's intention is described in Japanese Patent Application Publication No. 2004-257434 (JP-A-2004-257434). In the system as described in JP-A-2004-257434, the absolute value of the vehicle acceleration is integrated for each given period of time so that the integral is updated. When the integral is larger than a first reference value, a first shift schedule is changed to a second shift schedule in which shift lines in a region of at least a part of the first shift schedule are changed to higher-vehicle-speed shift lines, and shift control is performed based on the second shift schedule.
In addition, a system configured to change the content of shift control in accordance with the degree of sportiness is described in the proceedings 944 1994-10 (p. 241-p. 244) of academic symposia held by the Society of Automotive Engineers of Japan. The system is configured to change the vehicle speed according to the gradient of the road and the manner of driving, and is configured to determine the manner of driving based on the degree of sportiness. The degree of sportiness is determined based on the larger value of the engine load and a degree of tire load, where the degree of tire load is represented by a degree of load relative to the limit friction force of the tire.
Although the systems described in JP-A-06-249007, JP-A-11-129924, JP-A-09-242863, JP-A-07-156815, JP-A-2008-120172, JP-A-004-257434, and the proceedings 944 1994-10 (p. 241 -p. 244) of academic symposia held by the Society of Automotive Engineers of Japan execute control that reflects the driver's intention regarding running, the systems leave room for improvement.